This section provides background information related to the present disclosure which is not necessarily prior art.
In recent years, the motion capture technology is widely used in motion capture and motion analysis for sports. The motion capture technology can digitally record actions of the object, and the common motion capture technology at present mainly includes an optical motion capture and an inertial sensor based motion capture.
The optical motion capture system usually includes 4 to 32 cameras which are arranged around an object to be measured, and a motion range of the object is within the overlapped area of the cameras. Some special reflective points or luminous points are affixed to the key parts of the object to be measured, to serve as markers for visual identification and processing. After the system calibration, the cameras continuously shoot the motion of the object to be measured, store the image sequence, analyze and process the stored image sequence, and calculate the spatial position of each marker point at a certain moment, so as to obtain the accurate trajectory. The advantage of the optical motion capture is that there is no limitation of mechanical devices, wired cables, etc., thereby allowing a large motion range of the object, and the sampling frequency is high, and thus the optical motion capture may meet the requirements of most sports measurements. For this system, however, the price is high, the calibration is tedious, and only the object motion in the overlapped area of the cameras can be captured. In addition, in case of complex motion, the markers are easily confused and occluded to cause a wrong result.
The traditional mechanical inertial sensors have been applied for the navigations of aircrafts and ships for a long time. As the Micro Electro Mechanical System (MEMS) technology develops rapidly and the technology of micro inertial sensor continues to mature, in recent years, people start attempting the motion capture based on micro inertial sensor. The basic method is that the object to be measured is connected to an Inertial Measurement Unit (IMU) which moves with it. The inertial measurement unit usually includes a micro accelerometer (measuring an acceleration signal) and a micro gyroscope (measuring an angular velocity signal), and the position information and the orientation information of the object to be measured can be obtained through a quadratic integration of the acceleration signal and an integration of the gyro signal. Due to the application of the MEMS technology, the size and weight of the IMU may be very small, thus the influence on the motion of the object to be measured is slight, and the site requirement is low, the allowed motion range is large, and the system cost is low.
Due to small volume, light weight, low price, etc., the MEMS inertial sensor presently has been applied in the capture and analysis of some sports, such as a golf swing motion. Specifically, a sensor module is mounted to a hand-held sports appliance through a certain fixture structure, and the sensor module moves with the apparatus during motion, captures the motion of the apparatus and wirelessly transmits the captured data to a certain terminal receiving device. This mode based on the single-node motion capture has a low cost, but it only captures the motion of a sports appliance, and is unable to provide the motion data of a human body.
U.S. Pat. No. 7,689,378 reveals a highly miniaturized motion capture system containing an MEMS sensor, and it can be embedded into a sports appliance without influencing the motion characteristics thereof. The motion capture module includes one tri-axial accelerometer, one tri-axial gyroscope and one tri-axial magnetometer, wherein the tri-axial accelerometer and the tri-axial gyroscope can measure the three-dimensional displacement and the three-dimensional orientation of the module relative to the external fixed coordinate system, and the tri-axial magnetometer can measure an absolute space of the module in conjunction with the tri-axial accelerometer based on the local geomagnetic vector and gravity field. The solution is implemented by integrating a single sensor module to a sports appliance (e.g., golf clubs), so as to capture the trajectory of the sports appliance and wirelessly transmit it to a receiver. In the mode based on the single-node motion capture of the technical solution, the sensor module is semi-permanently mounted and fixed to the sports appliance in the mounting manner of mechanical integration; and each sports appliance needs to be integrated with a sensor module for a sport requiring multiple sports appliance, thus the cost is increased.
U.S. Pat. No. 8,589,114 discloses a single-node motion capture and analysis system, wherein a sensor unit comprising a tri-axial accelerometer and a tri-axial gyroscope is adjustably mounted onto a surface of a sports appliance; a motion of the sports appliance is captured, and one or more motion characteristic values are determined through processing of motion data; the motion data and motion characteristic values are wirelessly transmitted to a display unit, so as to be displayed in a graph form. An adjustable sensor mounting mode is adopted in the solution, so that the sensor unit can be flexibly mounted and removed, which facilitates the actual usage. But under the single-node motion capture mode of this solution, the sensor unit only is mounted to the sports appliance to analyze the motion of the sports appliance that is moving, and not capable of providing motion information of a human body.